Adsorption of tuberculin to glass

Dilutions of the purified tuberculin RT 19-21 (Statens Seruminstitut, Copenhagen) have been found to be subject to unsystematic variations in potency. Preliminary investigations suggested that adsorption of tuberculin on to the container might be the cause. This possibility has been further explored in a series of experiments on guinea-pigs that is reported in the present paper.IT IS DEMONSTRATED THAT TUBERCULIN IS, IN FACT, ADSORBED TO THE GLASS SURFACE OF THE CONTAINER: tuberculin-active eluates are obtained from ampoules previously used for tuberculin, with a buffer eluant containing Tween 80.Estimates indicate that a 5 TU dilution of RT 19-21 (prepared to contain 5 TU or 0.0001 mg per 0.1 ml) loses on an average 60% of its active substance through adsorption. The amount adsorbed differs from one ampoule to another, and a negative correlation is observed between the potency of the original contents of the ampoule and the potency of the eluate obtained when the ampoule is refilled with Tween 80 eluant.The extent of adsorption depends on the strength of the dilution, the temperature, and the duration and extent of contact between dilution and container. Another observation is that shaking of the ampoule reduces adsorption.There are indications that the purified tuberculin RT 19-21 is composed of at least two fractions of different adsorbability.It is pointed out that the accuracy of tuberculin testing would be markedly increased if adsorption from the tuberculin dilutions could be prevented.